This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Helicobacter pylori is a bacterium that colonizes the human stomach. The bacterium, along with the VacA protein toxin it produces, is important in the development of gastric cancer, the second leading cause of cancer-related death worldwide, and in peptic ulcer disease. We propose to determine the three-dimensional structure of VacA in an effort to understand this toxin?s mechanism of action. We have obtained crystals of VacA that diffract to 2.0 [unreadable] in-house. VacA is novel in that it does not share sequence homology with other known proteins. We plan to phase this structure by MAD methods and therefore access to a synchrotron beamline with tunable wavelengths is essential. We have prepared selenomethionine, platinum, and mercury derivitized crystals in preparation for these synchrotron MAD experiments. We also anticipate that the well-collimated beam and larger detectors offered at synchrotron beamlines will help us resolve spots from our 260 [unreadable] cell edge.